Method and circuit arrangement for detecting motion, direction and position of a part driven by an electric motor

ABSTRACT

An electric motor for driving a component, such as a vehicle window lifter or a machine tool, functions as a generator, when the motor drive voltage is switched off and the motor is short circuited. The motor keeps running due to inertia or other influences. During this period after switch-off a generator voltage and respective generator current are produced. The generator current is measured for various purposes, preferably in combination with a measured r.p.m. signal. The generator current signal alone, or in combination with the r.p.m. signal, is evaluated to provide information regarding the motion of the driven component including information regarding the motion direction and position of the component.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Continuation-In-Part application of U.S.Ser. No. 09/433,191, filed on Oct. 25, 1999 now abandoned.

PRIORITY CLAIM

This application is based on and claims the priority under 35 U.S.C.§119 of German Patent Applications No. 198 55 996.8, filed on Dec. 4,1998, and No. 198 49 430.0, filed on Oct. 27, 1998, the entiredisclosures of which are incorporated herein by reference through theparent case U.S. Ser. No. 09/433,191 the priority of which is alsoclaimed under 35 USC 120.

FIELD OF THE INVENTION

The invention relates to monitoring a part driven by an electric motor.The part may, for example, be a motor driven vehicle window or a tool.In many instances it is desirable to provide information whether a partdriven by an electric motor is moving, if so in which direction the partis moving, and which position has been reached. In the case of a vehiclewindow, especially a rear window, the respective information is used forcontrolling an electrically driven window lifter to provide ananti-jamming function. The invention also relates to a circuitarrangement for carrying out such monitoring.

BACKGROUND INFORMATION

A group of known devices for detecting the position and the direction ofrotation of a power driven part makes use of 2-channel sensor systemswhich provide signals that are phase-shifted and evaluated in anelectronic unit. The sensors used can operate in accordance withdifferent physical principles, e.g. electrical, magnetic, inductive, andoptical.

For example, the electric motor drive disclosed in EP 0,359,853 Al makesuse of two Hall sensors displaced at an angle to each other andallocated to a ring magnet attached to an armature shaft. When thearmature shaft rotates, the two Hall sensors generate twocorrespondingly phase-shifted signals that are digitized and thenevaluated in an electronic unit. After processing, the respectivesignals represent the only basis for identifying the direction ofrotation. Since the corresponding signal pattern is characteristicallydifferent for each direction of rotation, the counted pulses can beallocated unequivocally to a definite direction of rotation.

However, the known technical solution mentioned above requires no fewerthan two sensor channels, whereby it needs a correspondingly high numberof components and conductors for its implementation. Also, theconstruction space to be provided for the installation can have anegative effect, especially when using small drive units with integratedelectronics.

When only one such sensor is used, only one signal exists which isproportional to the number of the revolutions made by the motor andwhich is then allocated to one direction of motion of the driven part inaccordance with the polarity of the motor drive voltage. The signal mustbe added to or subtracted from the previous position, whichever applies.Signal flanks that occur after the motor drive voltage has been switchedoff cannot be assigned.

Japanese Patent Publication JP 63-304307 A discloses a velocity controlfor a motor drive wherein the phase difference between a velocitycontrol pulse and an incremental pulse of a length measuring laserdevice is continuously acquired. The control circuit used in saidJapanese disclosure further includes a pulse converter and a mechanismfor transforming the rotary motion of the motor into a linear motion. Anup or a down count signal is generated in a transformer from themeasurement of the linear motion in accordance with the direction of thepositioning command.

The teaching described above does permit a very accurate control of theadjustment velocity of a driven part but it is not suitable. forestablishing at the same time its position. Further measures must beprovided for this purpose.

Furthermore, German Patent Publication DE 43 15 637 C2 discloses amethod for detecting the position and direction of rotation of a drive.Not only the signal flanks of the digitized sensor signal but also thestatus of the drive is taken into account in that in the event of adirection reversal of the rotation the signal flanks are allocated inaccordance with an overshoot time that is limited by fixed timethresholds. On principle, these time thresholds can be determinedempirically or calculated mathematically. Adaptation to widely varyingsystem conditions is not possible because the variation of the motorcurrent over a period of time when the direction of rotation reverses,varies by several orders of magnitude. In particular, a control withfixed thresholds is always limited solely to a specific load situation,which is essentially determined by the external moment to be overcome. Acurrent rise due, for instance, to a window pane freezing or jammingdoes lead to deviations. In motor vehicles, the operating supply voltagecan drop quite considerably if the battery is about dead and otherelectrical power using elements are also being operated. If the electricmotor is used very frequently, as is the case, for example, in actuatingdrives on industrial machine tools, the electrical parameters of themotor also change because of the warming effect. If the time thresholdswere to be placed so far apart that all these cases could still bedetected, then a particularly smooth running actuator arrangement wouldperform several revolutions in the opposite direction before beingdetected by the threshold. 0,603,506 A2 describes a method fordetermining with a position encoder the position of a part driven in twodirections by an electric motor in motor vehicles, wherein a change inthe movement direction is to be identified according to the duration ofa break period between two pulses from the position encoder.

Errors can occur in such a method due to a rapid change of direction orif the motion of the part is non-uniform and does not take place in asingle step.

The applicant's DE 197 33 581 C1, which is not a prior publication,describes a method for measuring the motor current at the latest at thetime of driving switching devices for the purpose of switching over themotor voltage from one direction of motion to the opposite direction. Onchanging the polarity of the externally supplied motor drive voltage,the motor current displays a characteristic curve due to the overshootas a result of the mass inertia of the motor and the part moved by it,for instance the window pane and its mechanical drive transmission. Avoltage that opposes this reversal of direction of motion is induced andsuperimposed on the external motor drive voltage and causes thecharacteristic curve of the motor current from which the actual momentin time for the reversal of direction of motion is derived as a functionof time, which is considerably later than the time at which the motordrive voltage changes over. The signal flanks of the sensor signal areadded to or subtracted from the actual position by the signal evaluationaccording to the actual direction of motion. This electromechanicalbehavior of d.c. motors is described by means of so-called motorequations.

In a series of tests it has been found, however, that because of othereffects, deviations continue to occur in the position determination.These deviations are not negligible and cumulate over the life of avehicle.

A substantial cause for the above mentioned deviations that continue tooccur in the position determination are signal flanks that arise evenafter switching off the motor drive voltage. Particularly, afterstopping the motor, an overshoot or run-out of the motor occurs becauseof inertia, which has been neglected heretofore. Such motor run-out can,however, continue for a duration corresponding to several motorrevolutions causing respective signal flanks which are not evaluated orwhich are incorrectly evaluated. Further, this fault is not alwayscompensated by a corresponding run-out in the opposite direction ofmotion.

The disclosure of Japanese Patent Publication JP 07-222477 A, publishedon Aug. 18, 1995 has recognized that each of these changes in the motorrotation direction results in a voltage induction in accordance with thegenerator principle. These deviations, however, occur when the motor isalready switched off from the motor drive voltage. Therefore, it ispossible to ascertain the generator voltage and to make possible anallocation of the generator voltage signal flanks to the actual motiondirection.

For a number of uses it is, however, necessary to stop the motor asquickly as possible. Such stopping takes place conventionally byshort-circuiting the winding terminals of the motor. A respectivecircuit arrangement for a braking action is, for example disclosed inU.S. Pat. No. 4,319,170. However, the rotation direction of the motor isnot taken into account in the known braking action circuit.

As is disclosed in said JP 07-222477 A, the generator voltage cannot bemeasured or ascertained during the existence of the short-circuit.Therefore, it is suggested in Japanese publication JP 07-222477A to openagain briefly the switches that short-circuit the motor to cause a briefno-load run and to measure and evaluate the generator voltage thatoccurs during this no-load run. Such a temporary ascertaining of thegenerator voltage, however, requires a noticeably increased effort andexpense for the motor control and delays the braking action of themotor. Moreover, the method according to the above Japanese publicationis still subject to deviations due to erroneous allocation of signalflanks.

OBJECTS OF THE INVENTION

In view of the foregoing it is the aim of the invention to furtherimprove and to simultaneously simplify a method for recognizing themotion, the motion direction and the position of a component that isdriven by an electric motor, which for example, opens or closes a carwindow. It is also an object to provide a circuit arrangement for theperformance of said method. Another important object of the invention isto determine the rotation direction of an electric motor that has beenshort-circuited for applying a quick braking action to the electricmotor without the need for any temporary interruption of theshort-circuit of the motor.

SUMMARY OF THE INVENTION

A motion direction of a component drivable by an electric motor isdetected according to the following steps. First, the electric motor isswitched on for rotation in a desired direction of rotation by applyinga respectively polarized motor drive voltage to the windings of theelectric motor. Second, the polarized motor drive voltage of theelectric motor is switched off and the electric motor is simultaneouslyshort-circuited while the motor keeps running by reason of inertiawhereby the motor temporarily operates as a generator which generates orinduces a generator or inertia current. Third, the induced generatorcurrent or inertia current of said electric motor following theswitch-off is measured or sensed to provide a motion signal thatcontains motion and motion direction information regarding the motion ofthe drivable component. The motion direction is based on the polarity ofthe induced generator current. Fourth, the motion signal is evaluated toobtain said motion and direction information for further use, such ascontrolling the motor. Short-circuiting the motor while measuring orsensing the inertia current has the advantage that the time duration ofcontinued rotation following switch-off is reduced and the circuitarrangement is simplified.

According to the invention there is further provided a circuitarrangement for measuring an induced generator current that is producedby inertia rotation of an electric motor following stopping saidelectric motor by short-circuiting. The present circuit arrangementincludes the electric motor, a drive voltage source (U_(B)) and areference potential connectable or connected to the motor throughswitching devices for operatively connecting windings of said electricmotor to said operating voltage source and to said reference potentialfor normally driving said electric motor to rotate in a desired rotationdirection. At least one voltage drop producing electric circuit elementsuch as a measuring resistor or a diode or even a diode inherent in theswitching devices is operatively connected to the electric motor. Theswitching devices are further connectable for short-circuiting theelectric motor through the at least one voltage drop producing electriccircuit element for inducing a voltage drop that is proportional to theinduced generator current. At least one electric measuring circuit isconnected to the voltage drop producing electric circuit element formeasuring the voltage drop and for producing a measured signalrepresenting the induced generator current.

By short-circuiting the drive motor for applying a breaking action andmeasuring an induced generator current also referred to as inertiacurrent that is generated by the motor run-out caused by inertia, theinvention achieves the important advantage that the generator currentcan be continuously measured during the run-out without interrupting theactive braking action applied to the motor. More specifically,interrupting the short-circuiting of the motor is avoided. Further, bymeasuring the generator current during run-out following theshort-circuiting a more precise control is assured because a number ofdeviations are now taken into account which heretofore wentunrecognized. As a result, sensed signal flanks are correctly allocatedto the respective movement direction. Thus, the method of the inventionis capable of taking into account deviations that can be caused byexternal forces outside the drive system for the operation of the motordriven component such as a car window. For example, mechanicalvibrations which move the component, or a spring-back action when thecomponent encounters a stop, can cause such deviations. Any structuralelements such as rubber dampers inside the motor, tension springsforming enclosures of a cable pull connecting the motor to the movablecomponent or rubber buffers or seals have a certain elasticity that cancause the spring-back action, since these elements are first tensionedby the run-out of the motor whereby energy is stored and then dissipatedby causing the spring-back action. Any deviations caused by the abovementioned structural elements are taken into account by the invention.

Further embodiments of the present method take all run-out andspring-back characteristics of the component drive system into accountas well as the motion direction of the driven component prior toswitch-off and any motion in the opposite direction due to saidspring-back. Moreover, other movements of the motor can be detected.Such other motor movements are, for example, caused by mechanicalforces, while the motor drive voltage is switched off. The features ofthe further embodiments are capable to take such motor movements intoaccount. Once the motion direction is ascertained and known the signalflanks of the sensor output signals can be added to or subtracted fromthe previous component position thereby providing motion directioninformation.

The circuit arrangement according to the invention comprises in theshort-circuit branch an electrical circuit element for producing avoltage drop between the motor winding terminals which are shortcircuited for stopping the motor. For example, separate measuring shuntresistors can be used for this purpose. In another embodiment theinternal resistance of a circuit element, particularly the motorswitching device, is capable of producing a sufficiently large voltagedrop that can be used for the present purposes.

The measuring resistor may be divided into several measuring resistors.Instead of providing the measuring resistor or shunt resistor as one ormore separate circuit components, it is possible to provide themeasuring resistor in the form of a printed circuit resistor. In anotherembodiment the voltage drop is measured across a diode which isconnected to the circuit to be conducting in the generator current flowdirection so as to pass the generator current that is produced as aresult of short-circuiting the motor. The conductive state voltage dropacross the diode is approximately 0.7 volts which corresponds to thegiven threshold generator voltage. Compared to measuring a voltage dropacross a resistor, the diode has the advantage of a considerably lowerinternal resistance. In both instances the voltage drop is a measure forthe respective generator current.

The present circuit arrangements permit not only measuring of thegenerator current. Rather, the present circuits can also be used formeasuring the motor drive current when the motor drive voltage isapplied, in particular also for detecting the time at which a reversalof a motion direction takes place when changing the direction of themotor drive voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be clearly understood, it will now bedescribed in connection with example embodiments, with reference to theaccompanying drawings, wherein:

FIG. 1 shows a schematic circuit arrangement for switching off andshort-circuiting an electric motor M for detecting the motion, thedirection of motion and the position of a component that can be moved bythe electric motor M;

FIGS. 2a to 2 f are time charts of the sensed or measured signal 3.S fordifferent motions;

FIG. 3 shows another example embodiment of the present circuitarrangement;

FIG. 4 illustrates a circuit arrangement with four switching devicesconnected in an H bridge to the motor with a shunting diode poled in thereverse direction in each bridge branch;

FIG. 4a shows a switching device of a MOSFET-transistor arrangement withthe substrate connected to the source thereby inherently forming adiode;

FIG. 5 illustrates the measuring voltage curve before and after stoppingthe motor, for a circuit according to FIG. 4; and

FIG. 6 shows the timing for driving the switching devices in accordancewith FIGS. 4 and 5.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BESTMODE OF THE INVENTION

FIG. 1 shows schematically a circuit arrangement for detecting themotion, the direction of motion and the position of a component or partthat is drivable by an electric motor M. The motor M is connected on theone side by two switching devices S₁, S₂ to the motor drive voltageU_(B) and on the other side to the reference potential (ground ⊥). Fordriving the motor by the motor drive voltage U_(B) one of the twoswitching devices S₁ or S₂ is connected to the source of the drivevoltage U_(B) and the other switching device S₂ or S₁ is connected tothe reference potential such as ground ⊥. Thus, the motor M is driven bya polarization of the motor drive voltage U_(B); this polarization canbe set by the switching devices S₁, S₂ to correspond to a desireddirection of motion. In the shown position of the switches S₁, S₂ themotor M is short-circuited. More specifically, to switch off the motorM, both switching devices S₁ and S₂ are connected to the referencepotential such as ground so that no further external motor drive voltageis applied to the motor M.

The switching terminals of the switching devices S₁, S₂ connected to thereference potential are short-circuited through a shunt resistor R₂ andlinked through a measuring resistor R₁ to the reference potential ⊥ sothat the junction point JP between R₁ and R₂, to which all switchingpoints are connected, is always connected to the reference potential.Other embodiments of a circuit component that suitably produces thevoltage drop representing the generator current, are described inconjunction with FIG. 4.

The measuring circuit 3 is realized in this example embodiment as anamplifier circuit which measures the voltage drop UM_(M1,2) across R₁and R₂ relative to the reference potential ⊥. To further simplify thefollowing signal processing, the amplifier is operated with an offsetvoltage U_(offset) which makes it possible, on the basis of the positiveamplitude, to evaluate a signal that has been shifted into the positiverange instead of a signal that is subject to polarity (+, −). Theevaluation unit 2 performs for this purpose, for example, an analog ordigital comparison with threshold values, correlates the signal flanksof the sensor signal 1.S with a direction of motion and changes therelevant position counter 4 accordingly. The time at which the motion ofthe component ends can also be ascertained from the measured generatorcurrent by interpolation from individual, measured points.

FIG. 1 shows by dashed lines another possibility in which a measuringresistor R₃ is connected in series with the motor M between theswitching devices S₁, S₂. The voltage drop U_(M3) across a respectiveresistor R₃ is supplied to a measuring circuit arrangement. Thisembodiment is possible without more, but the voltage drop U_(M3) has nodirect reference potential and therefore floats so that correspondinglyhigh-quality differential amplifiers must be used in the measuringcircuit arrangement with an effective common-mode suppression, whichinvolves higher costs. The generator current can, however in principle,be measured equally well by the measuring resistor R₃ whereby amovement, the direction of the movement and the position of thecomponent can be determined from the signal flanks occurring when themeasurement is made.

In this example embodiment of FIG. 1, the motor M drives a magneticrotor with magnetic polarities N=north, S=south. A Hall sensor 1 ispositioned for sensing the rotation of the magnetic rotor to generate asignal 1.S proportional to the number of motor revolutions that havetaken place. Other types of sensors, such as an electricaltouch-sensitive pulse generator or similar sensors may be used. However,this revolution signal 1.S does not permit any unambiguous correlationbetween the measured signals and a direction of motion. While the systemis being driven by means of the motor drive battery voltage U_(B), itcan generally be assumed that the direction of motion corresponds to theselected polarity of the motor drive voltage. If the motor drive voltageU_(B) is switched off, however, this correlation is no longer entirelycertain because, apart from overshoot effects due to inertia,spring-back or similar effects can occur.

If a movement of the motor or of the movable parts coupled to the motoroccurs while the motor drive voltage U_(B) is switched off as shown inFIG. 1, a generator voltage U_(ind) is induced which, due to theshort-circuit, leads to a measurable generator current I_(ind) flowingthrough a shunt R₂. The direction of this current I_(ind) corresponds tothe direction of the movement. There is a corresponding voltage dropacross the shunt R₂ and this voltage drop is measured by a measuringamplifier 3. Due to the offset voltage U_(offset), the amplified outputsignal 3.S will always be greater than zero in the range essential forthe measurement. Since only the motion as such and its direction need bederived from the signal 3.S, the accuracy of measuring the size of thevoltage drop is not critical.

The resistance R₁ and the measurement of the voltage drop U_(M1,2)across R₁ and R₂ makes it possible for the measuring arrangementincluding the measuring amplifier 3, to also measure the motor drivecurrent that flows through R₁ or through R₁ and R₂, depending on theposition of the switching devices S₁, S₂, even when the motor drivevoltage U_(B) is applied during normal operation. This possibility isanother advantage of the invention since it permits, for example,monitoring the drive motor operation.

If a motor is to be operated with several drive voltages or the numberof windings is to be changeable by selecting certain motor windingterminals from several winding terminals, the shunt R₂ must always bearranged between those switching points that are provided for switchingoff the motor drive voltage. If there are sevaral such points, each mustbe equipped with a shunt R₂. However, since at any one time only oneswitching constellation (ON or OFF) can be assumed, a suitably adaptedmeasuring arrangement could measure all shunts in parallel, for instanceby means of an open-collector circuit or the like.

The signal-time diagrams shown in FIG. 1, illustrate the signal 1.S fromthe Hall sensor 1, the signal 3.S representing the voltage drop U_(M1,2)across R₁ and R₂, and the signal 4.S at the output of the positioncounter 4.1 and facilitate clarifying the functions.

At the time t₀, current flows through the motor M with S₂ connected toU_(B) while S₁ is connected to the reference potential through R₂ andR₁. As the frequency or r.p.m. of the magnetic rotor increases, thesignal 1.S from the Hall sensor 1 shows signal flanks corresponding toan increasing r.p.m. of the motor M. The voltage drop UM_(1,2)represents at this time the motor drive current. At time t₁, the motordrive voltage U_(B) is switched off by switching both of the switchingdevices S₁, S₂ to the reference potential ⊥. Due to the mass inertia,however, the motor overshoots in the previous direction of motion orrotation, so that in this example embodiment a voltage induction U_(ind)takes place which is in the opposite direction and a correspondingopposite generator current I_(ind) occurs. The opposite generatorcurrent I_(ind) diminishes quickly due to the very low-ohmic shunt R₂.Even so, between t₁ and t₃ a further total of, for example, three signalflanks occurs as measured by the Hall sensor 1. The number of signalflanks depends on the mechanical parameters of the driven system. If thedirection of the generator current I_(ind) is not detected, one could,at best, allocate these signal flanks occurring after switch-off, to therotation direction prior to switching off the motor drive voltage U_(B),or these flanks after switch-off must be ignored. However, by measuringthe generator current after the switch-off according to the invention,as a voltage drop U_(M1,2) across R₁ and R₂ the motion direction can beascertained. Referring to the signal 3.S initially a negative generatorcurrent flows between t₁ and t₂, but at time t₂ a zero crossing occursand thereafter, until t₃, the current I_(ind) has a positive amplitude.This occurs when, after overshooting in the old direction, a spring-backtakes place into the new opposite direction of motion. The last of thethree signal edges of signal 4.S that occur during t₁ to t₃ is thereforein the opposite direction. An incorrect assessment would lead each timeto a deviation amounting to two steps on the position counter 4. Whilethe motor is being driven externally from t₀ to t₁, the position counter4 increments and this continues between t, and t₂ because of theovershoot (+1, +1). The signal edge that occurs between t₂ and t₃ is,however, a spring-back (−1) which identifies the opposite direction ofmotion which the position counter 4 takes into account as (−1).

FIGS. 2a to 2 f are time charts of the measured signal 3.S provided atthe output of the measuring amplifier 3 for various motion situations ofan electrical window lifter that have been measured in this exampleembodiment. Driving systems other than window lifters such as machinetool drives can be equipped with a system according to the invention formeasuring the induced generator current following a short-circuiting ofthe respective electric drive motor for applying a braking action.

FIG. 2a represents the upward motion or closing motion of a car windowduring the time from t₀ to t₁. The motor drive current is measuredduring this period as represented by the signal 3.S based on the voltagedrop U_(M1,2). The signal 3.S initially rises rapidly because the motoris first stationary. The signal then drops as the speed builds up. Attime t₁, the motor is switched off manually or through software eventhough the window has not yet encountered an object, such as an upperstop or an obstacle. However, due to the mass inertia of the drivensystem, an overshoot occurs in the upward direction after switch-off andthis overshoot leads to a negative voltage drop at t₁ due to the inducedgenerator current. Due to the offset or biasing voltage, however, thisdrop is shifted into the positive zone and the residual peak drawn withdotted lines is not evaluated: rather, this residual peak is effectivelycut off. The item of importance for the evaluation is the sign of thegenerator current as represented in the amplitude of the measuredvoltage drop U_(M1,2) and the time taken until the voltage drop reachesthe zero level which is approached, for example, by corresponding upperand lower thresholds with a specific tolerance. The tolerances can beused to absorb the commutation noise that invariably occurs with themeasuring signal. Similarly, interpolation methods are conceivable fordetermining t₂ and t₃. Signal flanks occurring between t₁ and t₂ can beassigned unambiguously to the old direction of motion, namely therunning-up phase.

FIG. 2b shows the downward motion or opening of the window with aswitch-off either manually or by means of software at time t₁ whichleads to a positive voltage drop in accordance with the direction ofmotion because of the generator current between t₁ and t₂, so thatsignal flanks which occur between t₁ and t₂ can also be assignedunambiguously to the previous direction of motion, i.e. the downwardmotion.

FIG. 2c shows the curve of the measured signal 3.S for the case in whichthe drive motor is energized to rotate in the original direction eventhough the window has already encountered a stop or an obstacle. As canbe seen from the curve, the motor current or voltage drop decreasesbriefly and then rises rapidly because the motor is immediately blockedagain afer small tolerances or elasticities have been overcome and thespeed goes towards zero. Therefore, the current rises correspondingly att₅, limited solely by the internal ohmic resistance of the motor. Thisis also detected by the evaluation unit 2 and results in a hardware orsoftware switch-off of the motor drive voltage. In this case, thenegative voltage drop observed in FIG. 2a does not occur becauseovershoot is not possible when the motor is blocked. Times t₁ and t₂coincide in t_(½). By contrast, however, where several window panes areinvolved spring-back can be observed to a greater or lesser degreedepending on the tolerances and elasticities of the various structuralunits. Therefore, a positive voltage drop as a result of a generatorcurrent which at least drops below a threshold at time t₃ can also beobserved. Tests have shown that in individually tested drive systemssignal flanks did indeed occur during this period between t_(1,2) andt₃.

These signal flanks were identified as being backwards directed andcould, according to the present method, be taken into account in theposition counting.

FIG. 2d shows the situation when a slight impact occurs against anobstacle which might even give way elastically during an upward motionof the window, whereby the motor current rises at time t₅. However,depending on the upper switch-off threshold the motor is switched-offquickly. In this case, an overshoot can subsequently be observed in theold direction of motor rotation in accordance with the measured negativesignal amplitude between t₁ and t₂ followed by a swing-back between t₂and t₃. The rapid drop and subsequent rise to the normal signal levelobserved at t₄ immediately after switching on the motor drive voltage attime t₀ is due to a brief idling of the motor when, for example, sliptolerances are overcome between the individually moved drive components.

FIG. 2e shows that, by the circuit arrangement according to theinvention, not only the classical motor output and the motor stop can beobserved but also the sequences that occur when directly changing thepolarity of the motor drive voltage by altering the position of theswitching devices S₁, S₂ as taught herein. The voltage, which dropsacross the measuring resistor R₁ connected externally relative to themotor, becomes zero at t₆, but after the motor speed falls it rises inthe old direction of rotation and reaches a maximum at time t₇ which canbe evaluated as the time of direction reversal. The amplitude of thismaximum is highly dependent on the actual load moment and thresholdsshould preferably be derived from previous values. This circuitarrangement can thus also detect the time of direction reversal, whenchanging the polarity of the motor drive voltage without there being aneed for additional components for these two basically differentmethods, apart from the shunt R₂ in the short-circuit path. Inparticular, only one measuring arrangement with a measuring amplifier 3is required if the evaluation unit 2 is matched accordingly which isreadily possible, also in terms of software provided in the form of amicrocontroller or microprocessor.

FIG. 2f shows two different signal peaks f₁ and f₂ of the measuredsignal in the presence of mechanical disturbances such as those whichcan occur in the case of a window in a motor vehicle due to unevennessof the ground on which the vehicle travels or in the case of machinetool actuators due to vibration from other machines, etc. In particularwhen the motor drive voltage is switched off following t₁, the overshootcan be extended or shortened by such vibrations. The correct overshoottime t₂₁ for f₁ and t₂₂ for f₂ can, however, be determined precisely andsignal flanks that arise can be assigned or correlated to the respectivemotion direction without doubt.

It is also possible to detect, by measuring the generator current or itsvoltage drop, any movements that occur when the motor is stationary andthe motor drive voltage is switched off, and to detect the motiondirection to update the position counter accordingly. This feature hasthe advantage that in the case of machine tool actuators, for examplewhen a movable tool carrier arm is accidentally moved while replacing atool, an adjustment run becomes unnecessary.

FIG. 3 shows another circuit arrangement according to the inventionwithout a measuring resistor R₁. Instead, the shunt resistor R₂ isdivided and connected through a junction point JP to ground or referencepotential as shown at R_(2.1) and R_(2.2). The other end of theresistors R_(2.1) and R_(2.2) is connectable through the respectiveswitch S₁, S₂ to the corresponding motor winding terminal. The specialadvantage of the circuit of FIG. 3 is that while the motor drive voltageis connected the electrical resistance is the same in both directions ofrotation if R_(2.1) and R_(2.2) have identical resistances. Only onemeasuring amplifier 3 is necessary across one of the two shunts R_(2.1)or R_(2.2) to measure the generator current. However, for monitoring themotor drive mode two identical measuring amplifiers 3.1 and 3.2 arepreferred as shown and even necessary. These measuring amplifiers ofidentical design have a special feedback feature through resistors 5.1and 5.2, respectively. Again, offset voltages U_(off1) and U_(off2) areapplied in each case as a direct component across the resistors 8.1 and8.2 at the respective positive input of the measuring amplifiers 3.1 and3.2 which are constructed as operational amplifiers. The negative inputincorporates the feedback with a reference to reference potential ⊥across the resistors 6.1 and 6.2.

The outputs of the measuring amplifiers 3.1 and 3.2 can be coupledtogether as a “wired analog OR” by providing a diode 4.1 and 4.2respectively in the output circuits of the amplifiers, whereby only oneseparate input is required for connecting the evaluation unit 2 to theamplifiers 3.1 and 3.2, instead of two. However, the superimposed ORsignals must be allocated to the respective polarity of the connectedmotor drive voltage because these OR-signals do not differ from oneanother. In the generator mode, however, the current flows throughR_(2.1) and R_(2.2) in a loop so that the voltage drops measured againsta reference potential have an opposite sign and therefore only thepositive current signal is transferred. If the evaluation unit 2 has twoseparate inputs, however, the direction of motion can again be deriveddirectly from the signals of the measuring circuit i.e. the amplifiers3.1 and 3.2.

FIG. 4 shows another circuit arrangement for implementing the presentmethod. Four switching devices S₁₁, S₁₂, S₂₁, S₂₂ are connected in theform of an H bridge to the two winding terminals of the motor M. Theswitching devices S₁₁ and S₁₂ are connected to the motor drive voltageU_(B). The switching devices S₂₁ and S₂₂ are also connected to thereference potential ⊥ through a junction point JP and the resistor R₁.For energizing the motor M, either S₁₁ and S₂₂ are closed for drivingthe motor in one direction, or S₁₂ and S₂₁ are closed for driving themotor in the opposite direction.

The switching devices S₁₁, S₁₂, S₂₁ and S₂₂ are MOSFET transistors whosesubstrate terminal B is connected to the source S, such as a battery, asshown in FIG. 4a. FIG. 4a also shows in dashed lines that within theMOSFETs an inherent diode DI is formed which is connected in each casein the reverse direction from drain D to source S and thus conducts nocurrent when the switching device is open while the motor M rotates inthe opposite direction.

To illustrate the function, in FIG. 4 in place of the MOSFETs for theswitching devices S₁₁, S₁₂, S₂₁ and S₂₂ an equivalent circuit is showncomprising a switch SW₁₁, SW₁₂, SW₂₁ or SW₂₂. Each equivalent circuithas a respective internal resistor RI₁₁, RI₁₂, R₂₁ or RI₂₂. A diodeDI₁₁, DI₁₂, DI₂₁, or DI₂₂ is connected in parallel to the respectiveseries connection of the switch and resistor.

The speed-proportional signal flanks shown in FIG. 4 are measured by aHall generator 1 as shown in FIG. 1, but not shown in FIG. 4. The outputsignal from the Hall generator 1 is supplied to the evaluating unit 2which also is connected to the two measuring amplifiers 3.1 and 3.2which measure the voltage drop U_(M) across the diodes D₂₂ and D₂₁ inthe event of a short-circuit. Additionally during normal operation thevoltage drop across R₁ is measured. The evaluation unit 2 has outputsfor driving the switches SW₁₁-SW₂₂ and transfers the informationrelating to speed and direction of rotation derived from the signaledges of the Hall sensor signal and the respective voltage drop to theposition counter 4, please also see FIG. 1. The measuring amplifiers 3.1and 3.2 can have a voltage offset U_(offset1,2) which causes the voltagesignal U_(M), described in more detail below, to rise by this amountU_(offset) compared with the reference potential, see. FIG. 5.

The sequences that take place in accordance with the present method willnow be described with reference to FIGS. 4, 5 and 6; FIG. 5 shows thevoltage drop U_(M) that can be measured by the measuring amplifiers 3.2and FIG. 6 shows the time curve of the control of the switching devicesS₁₁ to S₂₂.

The motor M is to be stopped at time t₀. Before the stopping when t<t₀,the motor is driven in one direction of rotation when switches SW₁₂ andSW₂₁ are closed thus causing the motor drive current IA(t<t₀) to flowfrom U_(B) through SW₁₂ to the motor M and from there through SW₂₁ andR₁ to ground. The switches SW₁₁ and SW₂₂ are open and the inherentdiodes DI₁₁ and DI₂₂ are polarized in the reverse direction.

The drive current Ia(t<t₀) generates a voltage drop U_(M) acrossresistor R₁. This voltage drop is measured by the measuring amplifier3.2, as shown in FIGS. 4 and 5.

At time t₀, switches SW₁₁ SW₁₂ and SW₂₁ are opened while switch SW₂₂ isclosed, as shown in FIGS. 4 and 6. Due to the generator principle andthe mass inertia, the motor now produces a generator voltage which isshort-circuited to bring the motor to a rapid stop. This short-circuitis provided across the closed switch SW₂₂ and the diode DI₂₁ of theMOSFET switching device S₂₁, as indicated by the short-circuit currentI_(K)(t>t_(C)). The induced generator voltage is polarized opposite tothe polarization of the motor drive voltage (U_(S)→⊥) whereby diode DI₂₁becomes conductive to close the short circuit. The particular advantageof this bridging compared to a short-circuit across a shunt R₂ as shownin FIG. 1 is, for a voltage above the diode conductive-state voltage,the very low internal resistance of the diode DI₂₁ so that the voltagedrop exceeds the conductive state voltage by only an insignificantamount and a relatively high short-circuit current can flow thusstopping the motor in a correspondingly shorter time. If the voltagedrop across the diode falls at t₁ below a preset threshold U_(S), whichcan approximately equal the diode conductive state voltage U_(D) thesecond switch SW₂₁ connected to reference potential is also closed inthe short-circuit loop (see FIG. 6) which is connected in parallel todiode DI₂₁. The now measurable voltage drop U_(M) is a drop only acrossthe internal resistor RI of the switching device S₂₁.

At time t₂, the current reaches zero and the motor M stops. This can,however, be followed by a spring-back of the motor or associated drivecomponents so that again a generator voltage of opposite polarity occurswhich can always be measured across the internal resistor RI of theclosed switching devices S₂₁ and S₂₂ and further signal flanks thatarise can be correlated to a direction of rotation in accordance withthe sign of the induced generator voltage. If the mechanical componentsare designed appropriately, this spring-back can also be neglected bynot evaluating signal flanks that arise after t₁ or t₂ or by simplyassigning them all to the opposite direction of motion.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated that it is intended to coverall modifications and equivalents within the scope of the appendedclaims. It should also be understood that the present disclosureincludes all possible combinations of any idividual features recited inany of the appended claims.

What is claimed is:
 1. A method for detecting at least one motion direction of a drivable component driven by an electric motor, said method comprising the following steps: (a) energizing said electric motor for rotation in a desired direction of rotation by applying a respectively polarized motor drive voltage to said electric motor, (b) switching off said polarized motor drive voltage and simultaneously short-circuiting said electric motor while a rotor of said electric motor continues to rotate by reason of inertia thereby generating an induced generator current while the motor is short-circuited, (c) sensing, while said short-circuiting continues, said induced generator current to provide a motion signal that contains motion and motion direction information regarding said drivable component, and (d) evaluating said motion signal to obtain said motion and direction information for further use.
 2. The method of claim 1, further comprising the step of sensing flank signals generated by flanks of a signal that is proportional to an r.p.m. of said electric motor and counting said flank signals to provide position representing signals, and performing said evaluating step of said motion signal with reference to said position representing signals to further obtain present motion, direction and position information of said drivable component.
 3. The method of claim 2, further comprising allocating said flank signals occurring immediately following said short-circuiting, to said desired direction of rotation until a point of time when the induced generator current (I_(ind)) falls for the first time below a given threshold.
 4. The method of claim 3, comprising ignoring any flank signals occurring following said point of time when the induced generator current falls below said given threshold.
 5. The method of claim 3, further comprising allocating any flank signals occurring following said point of time when said induced generator current falls below said given threshold, to a motion direction opposite to said desired direction of rotation.
 6. The method of claim 3, further comprising allocating any flank signals occurring following said point of time to a motion direction that corresponds to the polarization of said induced generator current.
 7. The method of claim 1, further comprising the following steps; (a) switching off said polarized motor drive voltage while said motor is still rotating in said desired direction of rotation, (b) performing said simultaneous short-circuiting of said electric motor by an electric circuit element that produces a generator voltage drop (U_(M)) representative of said generator current flowing through said electric circuit element, (c) measuring said generator voltage drop (U_(M)), (d) measuring a time duration (t₀-t₁) during which said electric motor is still rotating by inertia in said desired direction of rotation following said switching off of said polarized motor drive voltage, (e) counting flank signals occurring during said time duration (t₀-t₁), and (f) allocating said flank signals to a respective motion direction.
 8. The method of claim 7, comprising using as said electric circuit element for said simultaneous short-circuiting of said electric motor a diode poled in a conducting direction for said generator voltage drop (U_(M)) and measuring said generator voltage drop (U_(M)) across said diode to obtain said induced generator current.
 9. The method of claim 8, further comprising the step of closing at the end of said time duration (t₀-t₁) when said inertia rotation ends, a further electric circuit element connected in parallel to said diode for monitoring further flank signals occurring following an end of said time duration (t₀-t₁).
 10. The method of claim 9, wherein said further flank signals are ignored in a determination of a motion direction.
 11. The method of claim 9, wherein said further flank signals are allocated to a motion direction opposite to said desired motion direction.
 12. The method of claim 9, comprising using an internal resistance of said further electric circuit element for causing a voltage drop having a polarity (+or −), and allocating said further flank signals to that motion direction which corresponds to said polarity.
 13. A circuit arrangement for measuring an induced generator current that is induced by inertia rotation of a rotor of an electric motor following stopping said electric motor by switching-off a polarized motor drive voltage and simultaneously short-circuiting said electric motor, said circuit arrangement comprising an electric motor, a drive voltage source (U_(B)) for providing said polarized motor drive voltage, switching means for operatively connecting windings of said electric motor to said operating voltage source and to a reference potential for normally driving said electric motor to rotate in a desired direction of rotation, at least one voltage drop producing electric circuit element operatively connected to said electric motor, said switching means being further disconnectable from said operating voltage source and connectable for said simultaneous short-circuiting of said electric motor through said at least one voltage drop producing electric circuit element for inducing a voltage drop that is proportional to said induced generator current, and at least one electric measuring circuit (3, 3.1, 3.2) connected to said voltage drop producing electric circuit element for measuring said voltage drop and for producing a measured signal representing said induced generator current while said motor is short-circuited.
 14. The circuit arrangement of claim 13, further comprising a sensor (1) for sensing a motor r.p.m. to provide a respective r.p.m. signal having signal flanks, a signal evaluating circuit (2) having a first input connected to said sensor (1) for receiving said respective r.p.m. signal, and a second input connected to an output of said at least one electric measuring circuit for receiving said measured signal representing said induced generator current, said signal evaluating circuit processing said r.p.m. signal and said measured signal for producing an output signal providing information regarding a motion, motion direction and position of a component driven by said electric motor.
 15. The circuit arrangement of claim 13, wherein said switching means comprise a first pair of switches (S₁₁; S₁₂) each having one terminal connected in common to said drive voltage source (U_(S)) and a further terminal connected to a respective winding of said windings of said electric motor, and a second pair of switches (S₂₁, S₂₂) each having one terminal connected to a junction point (JP), a resistor (R₁) connected to said junction point (JP) and to said reference potential, each switch of said second pair of switches (S₂₁, S₂₂) comprising a further terminal connected to a respective winding of said windings of said electric motor for driving said electric motor in a rotation direction which depends on which switch of each pair is closed and which switch of each pair is open, and wherein said at least one voltage drop producing electric circuit element comprises a diode (DI₂₁, DI₂₂) connected in parallel at least to each switch of said second pair of switches (S₂₁, S₂₂), and wherein each diode (DI₂₁, DI₂₂) is poled to be normally non-conductive toward said junction point (JP).
 16. The circuit arrangement of claim 13, wherein said switching means comprise switches (S₁₁, S₁₂, S₂₁, S₂₂) forming a first and a second pair of switches, each of said switches comprising an inherent internal resistance (RI₁₁; RI₁₂; RI₂₁; RI₂₂) for measuring said voltage drop across said inherent internal resistance.
 17. The circuit arrangement of claim 13, wherein said switching means comprise switches forming a first and a second pair of switches, and wherein each of said switches is an enhancement type MOSFET including an inherent diode formed by a source and substrate connection.
 18. The circuit arrangement of claim 13, wherein said voltage drop producing electrical circuit element comprises at least one measuring resistor connected to said at least one electric measuring circuit for measuring said induced generator current as a voltage drop across said measuring resistor.
 19. The circuit arrangement of claim 18, wherein said at least one measuring resistor (R₃) is connected in series with said motor (M) when said motor is short-circuited.
 20. The circuit arrangement of claim 18, wherein said at least one measuring resistor (R₂) is connected in parallel with said motor when said motor is short-circuited.
 21. The circuit arrangement of claim 18, comprising two measuring resistors (R_(2.1); R_(2.2)) both connected at one resistor end to said reference potential and at the other resistor end to a respective winding terminal of said electric motor through said switching means.
 22. The circuit arrangement of claim 21, wherein said two measuring resistors (RI₂₁; RI₂₂) are inherent in said switching means (S₂₁; S₂₂), and further comprising two electric measuring circuits (3.1; 3.2) connect to said windings of said electric motor.
 23. The circuit arrangement of claim 13, wherein said at least one voltage drop producing electric circuit element comprises a measuring resistor (R₂) connected to said motor (M) when said motor is short-circuited, and comprising a further measuring resistor (R₁) connecting said first mentioned measuring resistor (R₂) to said reference potential, and wherein said at least one electric measuring circuit is connected for measuring a voltage drop (U_(M1,2)) across both said measuring resistors (R₁, R₂).
 24. The circuit arrangement of claim 13, wherein said at least one voltage drop producing electric circuit element comprises one or more resistors having a low impedance.
 25. The circuit arrangement of claim 24, wherein said low impedance is less than 1 OHM.
 26. The circuit arrangement of claim 24, wherein said one or more resistors are part of a printed circuit.
 27. The circuit arrangement of claim 14, wherein said at least one electrical measuring circuit comprises an amplifier, an off-set biasing voltage source connected to one input of said amplifier for biasing said amplifier in such a way that any occurring voltage drop is shifted at least partly into a positive range to provide a positive output signal at an output of said amplifier connected to said signal evaluating circuit (2).
 28. The circuit arrangement of claim 13, wherein said at least one voltage drop producing electric circuit element is an inherent resistance (R₃) of the circuit arrangement, and wherein said inherent resistance (R₃) is connected in series with said electric motor.
 29. The circuit arrangement of claim 13, wherein said at least one voltage drop producing electric circuit element comprises two measuring resistors (R_(2.1); R_(2.2)) connected in parallel to said electric motor between said reference potential and through a respective winding of said electric motor for producing a voltage drop. 